Method and electrochemical cell for synthesis and treatment of metal monolayer electrocatalysts metal, carbon, and oxide nanoparticles ion batch, or in continuous fashion

Abstract

An apparatus and method for synthesis and treatment of electrocatalyst particles in batch or continuous fashion is provided. In one embodiment, the apparatus comprises a sonication bath and a two-compartment chamber submerged in the sonication bath. The upper and lower compartments are separated by a microporous material surface. The upper compartment comprises a cover and a working electrode (WE) connected to a Pt foil contact, with the foil contact connected to the microporous material. The upper chamber further comprises reference counter electrodes. The lower compartment comprises an electrochemical cell containing a solution of metal ions. In one embodiment, the method for synthesis of electrocatalysts comprises introducing a plurality of particles into the apparatus and applying sonication and an electrical potential to the microporous material connected to the WE. After the non-noble metal ions are deposited onto the particles, the non-noble metal ions are displaced by noble-metal ions by galvanic displacement.

The invention claimed is: 
     
       1. An apparatus for depositing ultrathin films on a plurality of microparticles or nanoparticles comprising:
 a two-compartment chamber configured for submersion in a sonication bath, 
 the two-compartment chamber comprising an upper compartment and a lower compartment separated by a microporous material, and 
 the upper compartment comprising a cover, a working electrode, a Pt foil contact, a reference electrode and a counter electrode, wherein the working electrode is electrically connected to the Pt foil contact, and the Pt foil contact is electrically connected to the microporous material, 
 wherein the microporous material acts as a working electrode, and 
 wherein the microporous material working electrode serves to deposit the film on the microparticles or nanoparticles as the microparticles or nanoparticles pass from the upper compartment to the lower compartment. 
 
     
     
       2. The apparatus of  claim 1  further comprising a power supply configured to supply an applied potential to the working electrode. 
     
     
       3. The apparatus of  claim 2  wherein the power supply is operable to supply a voltage in a range of −1 to +1 Volts. 
     
     
       4. The apparatus of  claim 1  wherein the microporous material is selected from the group consisting of a carbon cloth, a reticulated glassy carbon, a microporous carbon material, and a Ti/Ru oxide fine gauze. 
     
     
       5. The apparatus of  claim 1  wherein the cell is adapted to maintain an atmosphere of inert gas. 
     
     
       6. The apparatus of  claim 1 , wherein the lower compartment comprises an electrochemical cell for containing a solution of metal ions. 
     
     
       7. A method for depositing ultrathin films on a plurality of nanoparticles comprising:
 (a) preparing an apparatus according to  claim 1  with an electrolyte having a predetermined concentration of ions of a non-noble metal to be deposited as an adlayer; 
 (b) introducing the plurality of nanoparticles into the cell; 
 (c) applying sonication to the cell; 
 (d) applying a predetermined potential to the microporous material electrically connected to the working electrode for a predetermined duration, whereby a non-noble metal adlayer is deposited onto the nanoparticles as they contact and fall through the microporous material; 
 (e) removing the nanoparticles having a non-noble metal adlayer from the lower compartment of the chamber; 
 (f) replacing the excess non-noble metal ions from the cell with an electrolyte having a predetermined concentration of ions of a more noble metal; 
 (g) reintroducing the nanoparticles having a non-noble metal adlayer from step (e) into the upper compartment of the chamber; 
 (h) applying sonication to the cell; and 
 (i) applying a predetermined potential to the microporous material electrically connected to the working electrode for a predetermined duration to deposit the more noble metal ions on the coated nanoparticles by galvanic displacement as the coated nanoparticles contact and pass through the microporous material, whereby the process of galvanic displacement results in nanoparticles coated with an adlayer of the more noble metal. 
 
     
     
       8. The method of  claim 7  wherein the nanoparticles are Pd nanoparticles. 
     
     
       9. The method of  claim 7  wherein the first and second applied potentials are between −1 and +1 Volts. 
     
     
       10. The method of  claim 7  wherein the predetermined duration is between 10 minutes to 2 hours. 
     
     
       11. The method of  claim 7  wherein an adlayer of up to one monolayer is deposited on the surface of the microparticles or nanoparticles. 
     
     
       12. The method of  claim 7  where in the sonication in both (c) and (h) are performed on a low setting for 10 minutes. 
     
     
       13. The method of  claim 7  wherein the non-noble metal ions are selected from the group consisting of Cu, Pb, Bi, Sn, Ce, Ag, Sb, and Tl. 
     
     
       14. The method of  claim 7  wherein the electrolyte of (a) is 50 mM CuSO 4  in a 50 mM H 2 SO 4  solution. 
     
     
       15. The method of  claim 7  wherein ions of a more noble metal are produced by adding a salt of one or more of PdCl 2 , K 2 PtCl 4 , AuCl 3 , IrCl 3 , RuCl 3 , OsCl 3 , or ReCl 3 , and whereby addition of the salt results in galvanic displacement of the material deposited as an adlayer by the more noble metal contained within the salt. 
     
     
       16. The method of  claim 7  wherein the electrolyte of (e) is 1.0 mM K 2 PtCl 4  in a 50 mM H 2 SO 4  solution. 
     
     
       17. The method of  claim 7  wherein the nanoparticles are processed as a batch. 
     
     
       18. The method of  claim 7  wherein the nanoparticles are continuously fed to the apparatus for depositing ultrathin films using a predetermined flow rate.